1. Field of the Invention
The present invention relates to measurement probes. More particularly, the invention relates to devices and methods used to detect and count heat cycles experienced by measurement probes.
2. Description of the Related Art
Control of industrial processes is largely dependent on measurement signals received from measurement devices within process mediums. Measurement probes, which are equipped with sensors such as pH sensors, temperature sensors, redox sensors, carbon dioxide sensors, and dissolved oxygen sensors, are frequently used to monitor biological and chemical processes in the fields of biotechnology, pharmaceuticals, and food/beverage processing. In such industries, accuracy of measurements is critical.
In such industries, sterilization or cleaning is also critical. Frequent sterilization or cleaning is often required in these industries, because bacteria and other microorganisms may proliferate on unsterilized surfaces and create health risks. Additionally, sterilization or cleaning of measurement probes is needed to prevent contamination deposits from building up on the surface of the probes where they can introduce errors into the measurement signals.
Three sterilization or cleaning methods are frequently employed to sterilize equipment used in biological or chemical processes: steam-in-place sterilization, clean-in-place, and autoclaving. Steam-in-place sterilization procedures allow for in-line pressurized steam sterilization of all surfaces located within the interior of a reaction vessel or other processing container (herein referred to as a processing vessel), thus providing for sterilization without disassembly. Clean-in-place procedures allow for in-line cleaning by flushing the process vessel and associated piping with sanitizing chemical solutions at elevated temperatures. Autoclaving involves subjecting the processing vessel and the entire probe, to pressurized steam heat within a separate autoclave chamber. Autoclaving is often a preferred method of sterilization at least in part when the processing vessel is relatively small and transportable to the autoclave chamber. The major drawback to autoclaving is that the entire probe body is subjected to the high sterilization temperature and this can have a detrimental effect on any internal circuitry that is powered up at the time. If the probes is externally powered then it must be disconnected from its signal and/or power cable before it is placed in the autoclave. In many industries, subjecting the process vessel, probes, and associated equipment to high pressure steam at 121° C. in an autoclave for 20-30 minutes is sufficient to achieve sterilization. However, it is not uncommon to find that the vessel, probes, and associated equipment are exposed to pressurized steam at temperatures in excess of 130° C. and for periods of 60 minutes or longer to insure complete sterilization.
Measurement probes can experience structural changes, aging, and decreased functionality and accuracy through exposure to extreme conditions. Particularly, the rapid increase and decrease of temperature associated with common steam heat sterilization or hot chemical solution cleaning methods leads to probe degradation; thus, measurement probes are consumable products which must be replaced regularly. In industry, a balance is required when determining how frequently to replace measurement probes. Premature exchange of probes unnecessarily increases costs, whereas a probe that has reached the end of its life may fail during use. Loss of the probe measurement in mid-process often results in loss of process control and the subsequent ruin of an entire biological or chemical batch, leading to costly waste and delays. Accordingly, it is important for the probe operator to monitor the condition and evaluate the fitness for service of industrial measurement probes by tracking the number of heat cycles that it has experienced.